Posted
by
kdawson
on Tuesday July 27, 2010 @02:58AM
from the one-proton-and-one-electron dept.

BraveHeart writes "Researchers have long known that mammals, including humans, lack a key enzyme — one possessed by most of the animal kingdom and even plants — that reverses severe sun damage. For the first time, researchers have witnessed how this enzyme works at the atomic level to repair sun-damaged DNA. 'Normal sunscreen lotions convert UV light to heat, or reflect it away from our skin. A sunscreen containing photolyase could potentially heal some of the damage from UV rays that get through.'"

Well, if it was present with all plants and animals (except mammals) why did evolution lose such a "useful" enzyme? Or more importantly, what functionality did the body get while losing it? Without understanding these basic questions, it would be foolhardy to get such a product and start using it all over our body.

IANAB but as far as I understand it photolyase only repairs a certain type of damage found between adjacent cytosine and thymine (or uracil) units. That just happens to be the type of damage most commonly caused by UV radiation, so the enzyme can be understood as a fix for that particular method of damage. Other forms of radiation or chemical carcinogens effect DNA in a variety of other ways, most of which photolyase won't have an affinity for, rendering it ineffective.

As a car analogy... photolyase is like caranuba wax. It'll fix the small scratches and minor dings, but if some jackass comes along and smashes your windows and kicks in your doors you won't have much luck trying to buff it out.:)

Except if you are in the sun a lot (ie enough to get burned), you probably should be using sunscreen otherwise you will get cancer even more quickly, and you're probably getting enough vitamin D in that case anyway (though I have no evidence to back this up).

Cancer is a disease that affects organisms late in life. Generally speaking, they will have already had an opportunity to reproduce by the time that they develop cancer. The introduction of this mutation could have been completely coincidental and it would not have affected the reproductive fitness of the organisms that had it.

I was about to post something similar to what you wrote, but you were quicker. I'd just like to add the minor point that while cancer isn't that bad for the reproductive success of a mammal, it's effect is not zero or entirely negligible. Since we're really talking about the self-replication of genetic data, which is what actually let's us explain close-kin relations on a biological level, cancer's effect and protection against cancer does have effects on the successfulness of one bundle of genetic data against another one.

Someone developing cancer at an older age loses the possibility of reproduction. A human male is more than capable of fathering an offspring over the age of 45. Dieing of cancer can also have a bad impact on the success of your offspring, because they lose the father's/mother's support. It's not only about an organisms' direct reproductive success, but also about the success of the genetic data that lives on in genetically closely related members of a species.

> Researchers have long known that mammals, including humans, lack a key enzyme -- one possessed by most of the animal kingdom and even plants -- that reverses severe sun damage

The story description is misleading. By careful omission it gives the impression that this enzyme is the only one that can repair sun-damaged DNA damaged by UV, emphasizing that humans lack it. OH CRUEL LORD! But we do in fact already have other enzymes that repair DNA damage and these are very old news. Ohio U. are just talking about one mechanism, but the press release makes it sound like the only one.

I'm not knocking either journal article. What they did was pretty cool, but would these people please learn to be honest in their press releases too? You would think they would have learned from Climategate?

Oh no. Not this armchair doctor thing again.* Vitamin D is NOT "the anti-cancer vitamin" It's a molecule that serves as a hormone to regulate calcium metabolism. It also happens to seem to help prevent some types of cancer, due to semi-related processes. But AFAIK, it has only DEMONSTRATED to reduce the incidence of colon cancer. For skin cancer, it has only been suggested.* In developed nations, most of us get way more vitamin D from enriched foods and such than we need. So there is no need to go jumping through hoops to get it. Specially hoops that involve you being exposed to a PROVEN carcinogenic (the sun). And even if you somehow DON'T want to believe we get enough vitamin D as-is, remember that to get your daily dose of vitamin D, you only need to expose your forearms (or the equivalent amount of skin) to th sun for 10 minutes. So trust me, even if you wear tons of sunblock, and spend your day under an umbrella, you WILL be getting more than enough vitamin D that way. Heck, you'll get it in the driving up to the beach before you even see the sea.* Melanoma (the most deadly form of skin cancer, and definitely right up there amongst the deadliest forms of cancer) is associated with repeated ACUTE sunburns (specially in childhood and early adulthood). Basaliomas and epitheliomas are amongst the most common forms of ANY cancer, and are not very deadly. In fact, when found, they often only need to be removed to treat them. These kinds of cancer are (proven, and causally at that) associated with CHRONIC sun exposure. Every little bit of sun counts for this one, as it has a cumulative effect.* Because of all of this, I think it is pretty stupid to recommend NOT to use sunblock (which would effectively be turning an acute sunburn into a minor exposure), specially when the reason is so that "you can synthetize more of the anti-cancer vitamin". It is also stupid to suggest that everything can be fixed by "taking a vitamin C dose after a sunburn". Where on earth did you get that from? What studies is this claim based on?

This is not to say, things wouldn't be better if people actually used sunblock correctly, or if instead of going to the beach you simply stayed in your mom's basement. But alas, IRL sometimes you need to go the beach to have a little social life. And when you do, you should wear sunblock. Even if you do so incorrectly, some is better than nothing, and even SUGGESTING you should forgo it completely in favor of taking some random pills hoping to cancel out cell damage is stupid, naive, and just irresponsible. I do agree that wearing hats, and long sleeves > sunscreen, but they are not mutually exclusive, you know... and then again, as I said, sometimes you go to the beach to have a good (semi-naked) fun time, not to go hide under a rock.

So please just keep your pseudoscience and personal choices to yourself. Or at least don't recommend people do the same. It's just stupid.

Fur covered body makes more sense as a replacement to cover such drift. Fur is pretty effective at blocking the sun. Also melanin. Mammals without fur and/or light colored skin get the shaft. Of sunlight.

Even though possession of melanin in large enough quantities is not longer a criminal offence, not even in Alabama, it universally is considered as an aggravating factor in any trial or police proceeding (see: treatment of 15-year-old drug users: 'young thug' vs 'young man with a promising future who just made a little mistake').

Someone developing cancer at an older age loses the possibility of reproduction. A human male is more than capable of fathering an offspring over the age of 45. Dieing of cancer can also have a bad impact on the success of your offspring, because they lose the father's/mother's support. It's not only about an organisms' direct reproductive success, but also about the success of the genetic data that lives on in genetically closely related members of a species.

That's all well and good, but consider that we're talking about the entire expanse of mammalian evolution, not the very short (and recent) period of time where being over 45 years old means you have more money and are likely to be more stable in life. Over the course of mammalian evolution, being over 45 meant you were an outlier.

Firstly, I'd like to point out how stupid the notion that "everything in nature MUST have a purpose" is. That is not what Darwin's theory is about at all, and yet people seem to have twisted evolution into some sort of sentient overmind orchestring everything towards some greater good (I'm not only referring to your post, this whole story is full of "well if mammals don't have the enzyme surely there's a reason!". But it's really a phenomenon that happens on almost every/. {and Digg's for that matter} story).Having said that, allow me to tell you why our (caucasians') skin has such a capacity: Because once upon a time, many thousands of years ago, caucasians actually LIVED on the Caucasus (and north-western Europe and Russia too, for that matter) where in winter, the sun is a VERY scarce resource, so much so that the efficiency of their skins to synthesize vit-D was just barely enough to get by; and therefore, people who couldn't synthesize enough Vit-D to remain healthy wouldn't reproduce and would eventually die off.End of story.

You can sit and ponder whether the recommended dosages are actually enough, but in all honesty, with all the years we've been using the scientific method as the backbone of medicine, we would have noticed by now if people who consumed larger amounts were living significantly longer (or developed superpowers, or whatever else you can think of)